The present invention provides a process for the gasification of carbonaceous materials to produce a high B.T.U. gaseous product. The process of the present invention is particularly useful for converting hydrocarbon-containing feedstocks to high B.T.U. gas by hydrogasification reactions.
Prior art methods of gasifying carbonaceous materials have primarily involved reacting a hydrocarbon feedstock and a hydrogen rich gas at elevated temperatures and pressures to produce a gaseous product containing methane and ethane as major components. The hydrogasification reactions are carried out in an empty reaction zone, as in the gas recycle hydrogenation process or in a fluidized bed, as in the fluidized bed hydrogenation process.
A major disadvantage of the above-mentioned processes is that the reaction is not thermally self-sustaining when high boiling, carbon-rich feedstocks such as reduced crude oils are gasified. The heat evolved by the hydrogasification of high boiling, carbon-rich feedstocks is not sufficient to maintain a minimum reaction temperature of about 1400.degree.F even when the reactants are preheated to the practical limit. It is possible to generate additional heat in the reaction zone by introducng an oxygen-containing gas into the reaction zone. This is not, however, a satisfactory method of operation because of the possibility of explosive reaction between oxygen and hydrogen gas which is also present in the reaction zone.
Another disadvantage of previous methods of hydrogasification is that the hydrogen required for the reaction is produced in a separate process such as, for example, partial oxidation of carbonaceous materials. The partial oxidation process produces a hydrogen-carbon monoxide gas containing at least 40 mole % hydrogen, at temperatures of 2000.degree.-3000.degree.F as a result of the partial combustion of the carbonaceous material with an oxygen-containing gas. The high temperature gas is conventionally cooled down to (1) separate a small amount of soot from the gas, (2) react carbon monoxide and steam to produce carbon dioxide and hydrogen, and (3) remove H.sub.2 S and CO.sub.2 from the gas to produce hydrogen-rich gas. When the partial oxidation process is used to produce hydrogen for hydrogasification processes, the hydrogen-rich product gas must be reheated to elevated temperatures suitable for the hydrogasification process. As a result, the heat contained in the high temperature partial oxidation generator gas can only be partially recovered as steam which cannot be effectively utilized in the plant and expensive fuel is consumed in reheating the hydrogen-rich gas for the hydrogasification process.
By the present invention there is provided a method for overcoming the above-mentioned disadvantages of previous methods. The process of this invention involves the following essential steps:
1. Partial oxidation of carbonaceous material with an oxygen-containing gas to produce a hydrogen-carbon monoxide gas at a temperature between about 2000.degree. and about 3000.degree.F;
2. Contacting high temperature gas from the partial oxidation generator with relatively cool, finely-divided carbon particles to produce a gas-solid mixture at a temperature between about 1500.degree. and about 2000.degree.F;
3. Introducing carbonaceous feed into the gas-solid mixture in a high velocity transfer line in which the contact time of the feed-gas-solid mixture is between about 0.05 and about 5 seconds, preferably between about 0.25 and about 1.0 second, so that hydrogasification of the feed is obtained; and
4. Separating solids from the gas-solid mixture at the outlet of the transfer line, cooling the separated solids, and returning cooled solids to mix with hot gas from the partial oxidation generator.
The high B.T.U. gases which may be produced by the method of the present invention are those gases having in excess of about 400 B.T.U. per cubic foot, and a specific gravity of about 0.5 to 0.8, preferably below about 0.70. Such a gas is generally known and is herein referred to as a high B.T.U. gas.